In the construction of aircraft, highly loaded frameworks comprising U-profiles or double T-profiles are built. Furthermore, bars with rectangular profiles are frequently used, for example, in the lower ribs of the center box of the vertical tail unit of the A380. While such profiles are suitable for constructing highly loadable frameworks, these bars will then however have to be relatively solid. This results in an increase in the weight of the highly loadable framework. In the case of relatively light loads, so-called SARMA® rods are used.1 For example, SARMA® rods are used for floor supports. However, due to their insufficient dimensioning, SARMA® rods are not suitable for highly loaded frameworks. 1SARMA® is an expired U.S. trademark of SKF Compagnie d'Applications Mecanique, Sur-Rhone, France.
Tube connection systems are known from the documents DE 199 21 690 B4, DE 20 2004 015 883 U1, DE 199 20 427 A1, DE 37 21 092 C2 and DE 20 2004 015 047 U1.
Buckling under pressure load is the critical load case for a brace/bar in a framework, because due to the moment-free design of frameworks, predominantly tensile forces or pressure forces are encountered. In spite of corresponding force distribution and force transfer to the entire framework, it is nonetheless possible for substantial individual pressure forces to act in individual braces, in particular in the case of substantial overall forces, acting on the structure.
In particular, at the so-called framework junction points, i.e., at the end of the framework bars, complex and heavy connections must be used.
In the case of aircraft, the center boxes of aircraft wings are, as a rule, subjected to substantial loads. In particular, the center boxes have to reliably transfer transverse loads and the associated bending loads to the aircraft fuselage. Since, as a rule, the center boxes comprise two opposite lateral surfaces, the bending load to which a center box is subjected results in a pressure load in one side surface and in a tensile force in the other side area perpendicular to a bottom panel to which the center box is attached. The center boxes are designed as box supports. That is, the construction of a center box comprises shells that are reinforced by spars, ribs and stringers. With the use of these components, local stiffening of the center boxes is to be achieved. However, in order to accommodate the substantial forces acting on the center boxes, the spars, ribs or stringers have to be of solid, i.e., of very heavy, construction.
In order to accommodate substantial forces, usually many large components are necessary. On the one hand, this results in disadvantages in the case of production errors because the large components have to be repaired at considerable expenditure. On the other hand, in particular by using ribs, it is not possible to transfer introduced loads, such as for example, loads that result from pressure forces or tensile forces during flight manoeuvres of an aircraft, in the shortest way to the fuselage connection. Thus, a known construction of a support structure for a center box, comprising spars, ribs and stringers attains great strength only if it is of a correspondingly heavy weight.